Metal halide discharge lamp containing tin and sodium halides

ABSTRACT

A tin halide lamp containing stannous chloride SnCl2, stannous iodide SnI2, and mercury which are almost completely vaporized in operation, an excess of tin for thermodynamic stability, an inert starting gas, and a predetermined small quantity of sodium chloride, bromide, or iodide exceeding the quantity vaporized. The lamp exhibits a continuous spectrum on which the broadened sodium D-lines are superimposed. The D-lines shift the color coordinates to the black body locus and simultaneously increase the efficacy for a superior combination of color rendition and efficiency without any reduction in life.

United States Patent 1 Kazek et al.

[451 May 6,1975

[ METAL HALIDE DISCHARGE LAMP CONTAINING TIN AND SODIUM HALIDES [75]Inventors: Gregory J. Kazek, Eastlake;

Dimitrios M. Speros, Painesville, both of Ohio [73] Assignee: GeneralElectric Company,

Schenectady, NY.

[22] Filed: Nov. 12, 1973 [21] Appl. No.: 414,807

Related US. Application Data [63] Continuation-impart of Ser. No.200,714, Nov. 22,

1971, abandoned.

[52] US. Cl. 313/229 [51] Int. Cl. H01j 61/18 [58] Field of Search313/184, 229, 225

[56] References Cited UNITED STATES PATENTS 3,279,877 lO/l966 Smith etal 313/229 UX 3,351,798 11/1967 Bauer 313/225 3,398,312 8/1968 Edris etal 313/229 X 3,566,178 2/1971 Mori et al. 313/229 3,586,898 6/1971Speros et al. 313/229 Primary Examiner-Palmer C. Demeo Attorney, Agent,or Firm-Ernest W. Legree; Lawrence R. Kempton; Frank L. Neuhauser [57]ABSTRACT A tin halide lamp containing stannous chloride SnCl stannousiodide SnI and mercury which are almost completely vaporized inoperation, an excess of tin for thermodynamic stability, an inertstarting gas, and a predetermined small quantity of sodium chloride,bromide, or iodide exceeding the quantity vaporized. The lamp exhibits acontinuous spectrum on which the broadened sodium D-lines aresuperimposed. The D- lines shift the color coordinates to the black bodylocus and simultaneously increase the efficacy for a superiorcombination of color rendition and efficiency without any reduction inlife.

6 Claims, 4 Drawing Figures Fig 1. 1

lnven tors: Gregor'g J. Kazek Dimvtrios MS eros by A Their A t t ;neg

PATENTEBMY 61375 2 345 SHEET 2 OF 3 WRVELENGTH AVELENGTH'A/ANoME TEBS400 450 500 550 600 650 700 750 lnvavtors: Gregory J. Kazek Dimktrios M.Spgaros b9 :7 :15, Their A'Ttofneg METAL HALIDE DISCHARGE LAMPCONTAINING TIN AND SODIUM I-IIALIDES REFERENCES TO RELATED APPLICATIONSThis application is a continuation-in-part of our earlier copendingapplication Ser. No. 200,714 filed Nov. 22, 1971, similarly titled andassigned, and now abandoned.

Cross-reference is made to copending application Ser. No. 121,141 filedMar. 4, 1971, by D. M. Speros,

R. M. Caldwell, and W. E. Smyser, entitled Metal Halide Discharge Lampand similarly assigned and now abandoned, and to copending applicationSer. No. 78,484 by D. M. Speros, R. M. Caldwell, R. H. Springer and R.P. Taylor, filed Oct. 6, 1970, entitled Tin Chloride Molecular RadiationLamp and similarly assigned.

BACKGROUND OF THE INVENTION The invention relates to high pressuredischarge lamps and more particularly to lamps of this kind containingmercury vapor and metallic halides.

The high pressure mercury vapor lamp which is extensively used foroutdoor and industrial lighting pro duces radiation concentrated in theyellow-green area of the spectrum. The distinct lace of radiation in theorange and red as well as in the blue results in poor color rendition.In recent years a radical improvement in both color rendition andefficiency has been achieved by adding to the mercury one or morevaporizable metal halides under proper control of loading, temperatureand pressure. Such improved lamps are described and claimed in US. Pat.No. 3,234,421 to Gilbert l-I. Reiling, issued Feb. 8, 1966. Thepreferred metal halides used in combination with mercury have beensodium iodide, thallium iodide and indium iodide. Although with thiscombination a remarkable improvement in efficiency and color renditionis achieved, the spectrum of the radiation nevertheless consistsessentially of the lines of the various metals superimposed on a weakcontinuum and is not equivalent to natural daylight.

In copending application Ser. No. 121,141 by D. M. Speros et al., filedMar. 4, 1971, entitled Metal Halide Discharge Lamp, and assigned to thesame assignee as the present invention, there are described and claimedhigh intensity arc discharge lamps of a molecular radiation type. Theselamps contain a filling of mercury, an inert starting gas, stannouschloride SnCI stannous iodide SnI and excess tin. In the discharge,molecular species are distributed over very closely spaced energy levelsin different electronic states between which radiative transistions mayoccur. The very closely spaced lines, or band spectra, characteristic oflow pressure molecular emission are practically masked at hightemperatures and pressures; thus there is produced a very broadcontinuum with the atomic lines of tin and mercury superimposed thereon.

SUMMARY OF THE INVENTION The object of the invention is to furtherimprove the color rendition and efficiency of the tin chloride molecularradiation lamp.

In accordance with the invention, we provide, in a high pressure gaseousdischarge lamp, a filling containing stannous chloride SnCl stannousiodide SnI and mercury in predetermined quantities which are nearly allvaporized in operation, an excess of tin for thermodynamic stabilityagainst attack of the tungsten electrodes by chlorine, an inert startinggas at a low pressure, and a predetermined quantity of sodium chloride,bromide, or iodide exceeding the quantity vaporized. The addition of thesodium D-lines to the preexisting spectrum shifts the color coordinatesfrom the green side of the black body locus substantially to the blackbody locus and simultaneously increases the efficacy for a superiorcombination of color rendition and efficiency without any reduction inlife. Due to the exceptionally high radiating efficiency of the sodiumatom, very litle sodium is required in the are for a sizablecontribution from it through the D-lines at 589.0 and 589.6 nanometers.In lamps according to our invention, the discharge sustaining fillingincludes per cubic centimeter of arc tube volume from about 0.15 to 0.70milligrams of SnCl from about 0.60 to 2.50 milligrams of Snl from about2.0 to 6.0 milligrams of mercury, at least 0.10 milligrams of tin, andfrom about 1.0 X 10 to 2.0 X 10 moles of sodium chloride, bromide, oriodide (0.06 to 1.17 mg. in the case of NaCl), and a small quantity ofinert ionizable starting gas.

Whether the fill ingredients are added as listed above or as relatedcompounds and elements should be determined on the basis of convenience.For instance it may be more convenient to add all or part of the Snl asI-IgI plus additional Sn metal to make up the molar quantity, in whichcase Hg is reduced by the corresponding molar quantity. Very soon afterthe lamp has gone into operation, an equilibrium will be established andit will be the same providing corresponding molar quantities have beenused.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates in side view a jacketedhigh intensity lamp embodying the invention.

FIG. 2 is a spectral energy distribution diagram of a typical tinchloride molecular radiation lamp without added sodium.

FIG. 3 is a spectral energy distribution diagram of a tin chloridemolecular radiation lamp having added sodium chloride in accordance withthe invention.

FIG. 4 is a chromaticity coordinate plot of lamps with various fillingsto which various quantities of sodium halide have been added in order topull the color cooordinates closer to the black body locus.

DETAILED DESCRIPTION OF INVENTION Lamp Structure Referring to FIG. 1, atin chloride vapor arc lamp 1 in which the invention is embodiedgenerally similar in construction and appearance to the high pressuremercury metal halide lamps sold commercially by applicants assigneeunder the trademark Multi-Vapor. The lamp comprises an outer vitreousenvelope or jacket 2 of ellipsoidal form having a neck portion 3 closedby a reentrant stem 4 through which extend stiff inlead wires 5,6. Theinleads are connected at their outer ends to the contacts of a screwbase 8 and at their inner ends to the inner arc tube 9.

The inner arc tube is made of quartz-like glass or fused silica and hassealed therein at opposite ends main arcing electrodes 11,12 plus anauxiliary starting electrode 13. The electrodes are supported on inleadswhich include intermediate thin molybdenum foil sections 14 hermeticallysealed through the flattened or pinched ends of the arc tube. The mainelectrodes 11,12 each comprise a double layer helix of. tungsten wirewrapped around a tungsten core.

The arc tube is supported within the outer jacket by a two-part mount,at the base end and 16 at the dome end. Each part comprises a pair oflongitudinally extending support rods bridged by metal straps 17 whichclamp about the pinched ends of the arc tube. The base end mount part iswelded to inlead 6 and serves as a conductor to main electrode 11. Thedome end mount part has attached thereto a spring collar 18 whichengages a reentrant nipple 19 in the dome end .of the jacket. Mainelectrode 12 is connected to inlead 5 by curving wire 21. Startingelectrode 13 is connected to inlead 5 through current limiting resistor22. A thermal switch 23 consisting of a bimetal is arranged to shortcircuit auxiliary electrode 13 to main electrode 11 after the lamp warmsup. Heat reflective coatings 24, suitably of ZrO are provided on the arctube ends to assure adequate heating.

By way of example of a preferred embodiment, in one lamp of 175 wattrating wherein the arc tube had an overall body length of about 6.30centimeters and a volume of about 4.60 cc., the fill consisted of 1.33milligrams SnCl 3.48 milligrams SnI 3.02 milligrams tin, 22.9 milligramsmercury, 0.60 milligrams sodium chloride, and torr argon at roomtemperature. It may be more convenient to introduce the fillings as tinchloride, mercury chloride, tin and mercury in which case equivalentmolar quantities are used as follows: 1.33 mg. SnCl 4.24 mg. Hgl 4.13mg. Sn, 21.0 mg. Hg and 0.60 mg. NaCl. Yet another alternative is tointroduce the filling as mercury chloride, mercury iodide, tin andmercury, in which case the equivalent quantities are 1.91 mg. HgCl 4.24mg. Hgl 4.96 mg. Sn, l9.6 mg. Hg and 0.60 mg. NaCl.

The spectral distribution diagram of the lamp of the previouslydescribed preferred embodiment is shown in FIG. 3 whereas the spectraldistribution for the same lamp without the added sodium chloride isshown in FIG. 2. The spectra differ primarily by the presence of thebroadened sodium D-lines at 589.0 589.6 nm. in FIG. 3 which are absentin FIG. 2, with substantially no change in the underlying continuum.

Examples of lamps constructed in accordance with our invention havedischarge sustaining fillings as given in Table 1 below. In each series,the parent or first lamp of the series has a tin chloride-iodide, tin,mercury filling which is modified in the derivative lamps by the ad-0.33 mg/cm Nal 0.13 mg/cm NaCl 0.89 mg/cm" Snl, 0.93 mg/cm Sn 4.98 mg/cmHg Lamp B Lamp B l Lamp B2 To B add 0.13 mg/cm NaCl 0.29 mg/cm SnCl To Badd 0.33 mg/cm Nal 0.76 mg/cm Snl 0.65 mg/cm Sn 4.98 mg/cm Hg Lamp CLamp Cl Lamp C2 0.39 mg/cm SnCl To C add 0.45 mg/cm Nal To C add 0.23mg/cm NaCl Lamp A Lamp Al Lamp A2 1.13 mg/cm Snl 0.65 mg/cm Sn 2.83mg/cm Hg Referring to FIG. 4, the chromaticity coordinates are shown forthe various lamps listed in Table l, in each case for the lamp beforeand after the addition of the sodium salt. The black body locus 31 isalso shown and it will be observed that in each case the addition of thesodium salt increases the x chromaticity coordinate to a verysubstantial extent, for instance by as much as 0.040, while havinglittle effect on the y chromaticity coordinate. The addition of thesodium salt shifts the chromaticity coordinate into close proximity withthe black body locus line.

It is important to limit the quantity of added sodium halide because itsvapor pressure is low but should some of the sodium be lost from the arctube, as by electrolysis through the quartz arc tube wall, the pressureof the halogen remaining behind would rise rapidly. In the case of addedNaCl, electrolysis of Na could cause a rise in chlorine pressure, suchrise in halogen pressure entailing violent failure of the lamp or rapiderosion of the tungsten electrodes. By limiting the sodium halide chargeto 2.0 X 10 moles or less per cubic centimeter of arc tube volume, suchpossibilities are substantially avoided. Another criterion for avoidingexcessive halogen pressure rise at end of life is a weight ratio of Nato Sn present in halide form not exceeding about 0.1. Fortunately theexceptionally high radiating efficiency of the sodium atom permits thedesired chromaticity shift to be achieved by small amounts of sodium notexceeding the foregoing limits. To achieve the desired chromaticityshift towards the black body locus in the temperature range from 3000 to5000K, the weight ratio of added Na to Sn preferably should be fromabout 0.07 to 0.09. The preferred weight ratio of SnCl to SnI for highefficiency coupled with reasonably long life is from about 0.3:1 to0.411.

The sodium requirement may be added to the lamp either as the chloride,bromide, or iodide, but depending upon the choice of halide in a givenSnCl -SnI lamp, a different equilibrium composition will result. Theintroduction of sodium halide to the lamp leads to the equilibrium SnCl(f) 2Nal(s) SnI (g) 2NaCl(s) Calculations based on thermodynamic dataand experimental observations indicate that for a lamp with a SnCl -SnI-Hg atmosphere prior to the addition of sodium halide, the minimumchange in equilibrium tin halide pressures is obtained when sodium isadded in the form of NaCl. Correspondingly it may be noted in FIG. 4that in every case a greater change is occasioned in the x coordinatewhen sodium is added in the form of iodide than when it is added in theform of chloride. A specific chromaticity coordinate and color renditionrequirment in an SnCl -SnI -Hg atmosphere may be satisfied using eitherNaCl or NaI as the additive, but the quantity will be slightly differentin either case and may require a readjustment in the proportions of theother fill ingredients. It may also be satisfied by the addition ofNaBr.

The efficacy of lamps embodying the invention such as lamps Al, A2, B1,B2, C1 and C2 is in excess of 70 lumens per watt. Efficacies up to about90 lumens per watt have been measured at color temperatures from 3000 to5000l(. This makes the lamp competitive with all other metal halidelamps in regards to efficacy and at the same time the lamp issignificantly superior in regards to color rendition.

The presence of sodium also has the desirable effect of lowering thepeak voltage at cyclical reignition. This means an improvement in powerfactor and the ability to operate on lower cost ballasts.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A high intensity discharge lamp exhibiting a substantially continuousspectrum in the visible range plus broadened sodium D line radiationcomprising a sealed elongated arc tube of light-transmitting material,

arc supporting electrodes mounted at opposite ends of said are tube oninleads sealed therethrough, and a discharge sustaining filling withinsaid are tube comprising per cubic centimeter of arc tube volume from0.15 to 0.70 milligrams of SnCl from 0.60 to 2.50 milligrams of Snl atleast 0. l milligram of tin, from 2.0 to 6.0 mg of mercury, from 1.0 X10 to 2.0 X 10 moles of one of sodium chloride, sodium bromide, sodiumiodide and mixtures thereof, and a small quantity of an inert startinggas.

2. A lamp as in claim 1 wherein the weight ratio of Na to Sn present inhalide form does not exceed about 0.1.

3. A lamp as in claim 1 wherein the weight ratio of Na to Sn present inhalide form is in the range of about 0.07 to 0.09.

4. A lamp as in claim 1 wherein the weight ratio of Na to Sn present inhalide form is in the range of about 0.07 to 0.09 and the weight ratioof SnCl to Snl is from about 0.321 to 04:1.

5. A lamp as in claim 1 wherein the weight ratio of Na to Sn present inhalide form is in the range of about 0.07 to 0.09 and the quantity ofsodium halide is selected to increase the x chromaticity coordinate andshift the color point of the lamp substantially to the black body locus.

6. A lamp as in claim 1 wherein the weight ratio of Na to Sn present inhalide form is in the range of about 0.07 to 0.09, the weight ratio ofSnCl to Snl is from about 0.311 to 04:1, and the quantity of sodiumhalide is selected to increase the x chromaticity coordinate and shiftthe color point of the lamp substantially to the black body locus.

1. A HIGH INTENSITY DISCHARGING LAMP EXHIBITING A SUBSTANTIALLYCONTINUOUS SPECTRUM IN THE VISIBLE RANGE PLUS BROADENED SODIUM D LINERADIATION COMPRISING A SEALED ELONGATED ARC TUBE OF LIGHT-TRANSMITTINGMATERIAL, ARC SUPPORTING ELECTRODES MOUNTED AT OPPOSITE ENDS OF SAID ARCTUBE ON INLEADS SEALED THERETHROUGH, AND ADISCHARGE SUSTAINING FILLINGWITHIN SAID ARC TUBE COMPRISING PER CUBIC CETIMETER OF ARC TUBE VOLUMEFROM 0.15 TO 0.70 MILLIGRAMS OF SNCL2, FROM 0.60 TO 2.50 MILLIGRAMS OFSNL2, AT LEAST 0.1. MILLIGRAM OF TIN, FROM 2.0 TO 6.0 MG OF MERCURY,FROM 1.0X10-6 TO 2.0X10-5 MOLES OF ONE OF SODIUM CHLORIDE, SODIUMBROMIDE, SODIUM IODIDE AND MIXTURES THEREOF, AND A SMALL QUANTITY OF ANINSERT STARTING GAS
 2. A lamp as in claim 1 wherein the weight ratio ofNa to Sn present in halide form does not exceed about 0.1.
 3. A lamp asin claim 1 wherein the weight ratio of Na to Sn present in halide formis in the range of about 0.07 to 0.09.
 4. A lamp as in claim 1 whereinthe weight ratio of Na to Sn present in halide form is in the range ofabout 0.07 to 0.09 and the weight ratio of SnCl2 to SnI2 is from about0.3:1 to 0.4:1.
 5. A lamp as in claim 1 wherein the weight ratio of Nato Sn present in halide form is in the range of about 0.07 to 0.09 andthe quantity of sodium halide is selected to increase the x chromaticitycoordinate and shift the color point of the lamp substantially to theblack body locus.
 6. A lamp as in claim 1 wherein the weight ratio of Nato Sn present in halide form is in the range of about 0.07 to 0.09, theweight ratio of SnCl2 to SnI2 is from about 0.3:1 to 0.4:1, and thequantity of sodium halide is selected to increase the x chromaticitycoordinate and shift the color point of the lamp substantially to theblack body locus.